RE: Paleo diet criticisms

From: gts (gts_2000@yahoo.com)
Date: Wed May 07 2003 - 22:37:52 MDT

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    I William Wiser wrote:

    > So the type of fat an animal is feed affects the composition
    > of it's own fat?

    Yes.

    > If that's true I find it interesting. I
    > don't suppose you have any references handy. I can search
    > but if you have any names or keywords...

    Below is an abstract describing some promising research on cattle diets.

    The "n-3" designation in this abstract refers to omega 3 oils and "n-6"
    refers to omega 6 oils. In this study, supplementing the cattle diet with
    high omega 3 linseed and fish oil had a dramatic effect on the balance of
    omega 6 to 3 in cattle muscle.

    We evolved on a ratio of omega 6 to 3 of about 2:1. Some even estimate the
    ratio to be 1:1. The modern American diet has swung way out of balance, with
    a ratio of about 10:1. Australia is even more out of balance with a ratio of
    about 12:1.

    This imbalance happened largely because we started feeding ourselves and our
    livestock high omega 6/3 ratio grains. Grains contain little fat, but what
    fat they do contain is weighted extremely in favor of omega 6 vs 3 when
    compared to the natural plant foods upon which humans and animals evolved.

    We feed high-carb, high-omega 6/3 ratio grains to our farm animals because
    it works well for purposes of fattening them up for slaughter. We feed
    ourselves more of the same and then we wonder why we're as fat as our farm
    animals.

    -gts

    Manipulating the fatty acid composition of muscle and adipose tissue in beef
    cattle.
    Br J Nutr 2001 Jan;85(1):115-24 (ISSN: 0007-1145)
    Scollan ND; Choi NJ; Kurt E; Fisher AV; Enser M; Wood JD
    Institute of Grassland and Environmental Research, Plas Gogerddan,
    Aberystwyth SY23 3EB, UK. nigel.scollan@BBSRC.ac.uk.
    Enhancing the n-3 polyunsaturated fatty acid (PUFA) content of beef is
    important in view of the generally saturated nature of fatty acids in
    ruminant meats and the negative effect this can have on human health. This
    study examined the effects of different sources of dietary n-3 PUFA on the
    performance of steers and the fatty acid composition of m. longissimus
    thoracis muscle and associated subcutaneous adipose tissue. Animals were fed
    ad libitum on grass silage plus one of four concentrates (60:40
    forage:concentrate on a DM basis) containing differing sources of lipid:
    Megalac (16:0), lightly bruised whole linseed (18:3n-3), fish oil (20:5n-3
    and 22:6n-3) and a mixture of linseed and fish oil (1:1, on an oil basis).
    Diets were formulated so that total dietary oil intake was 6 %,
    approximately half of which was from the experimental test oil. Linseed
    feeding not only increased the levels of 18:3n-3 in muscle phospholipid from
    9.5 to 19 mg/100 g muscle but also enhanced the synthesis of 20:5n-3, the
    level of which increased from 10 to 15 mg/100 g muscle. Linseed also
    increased the proportion of 18:3n-3 in muscle neutral lipid and in adipose
    tissue lipids by a factor of 1.64 and 1.75 respectively. Fish oil feeding
    doubled the proportion of 20:5n-3 and 22:6n-3 in muscle phospholipids. The
    proportion of 18:1 trans in muscle neutral lipid was higher on the n-3 PUFA
    diets than the control diet, 0.04 and 0.02 respectively. Despite the implied
    modification to rumen metabolism, lipid source did not affect feed intake,
    growth rate, cold carcass weight or carcass fatness, but carcass
    conformation score was higher on fish oil treatments (P < 0.05). However,
    total muscle fatty acid content was not different between treatments and
    ranged from 3.5-4.3 % of tissue weight. The increase in n-3 PUFA in the meat
    produced by feeding linseed or fish oil lowered the n-6:n-3 ratio but had
    little effect on the P:S ratio.



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